Process for the preparation of bis(perfluoroalkyl)phosphinic acids and salts thereof

ABSTRACT

The present invention relates to a process for the preparation of bis(perfluoroalkyl)phosphinic acids comprising at least the reaction of at least one difluorotris(perfluoroalkyl)phosphorane or at least one trifluorobis(perfluoroalkyl)phosphorane with hydrogen fluoride in a suitable reaction medium, and heating of the resultant reaction mixture. The invention also relates to salts of bis(perfluoroalkyl)phosphinic acids and to the use thereof.

The present invention relates to a process for the preparation ofbis(perfluoroalkyl)phosphinic acids comprising at least the reaction ofat least one difluorotris(perfluoroalkyl)phosphorane or at least onetrifluorobis(perfluoroalkyl)phosphorane with hydrogen fluoride in asuitable reaction medium, and heating of the resultant reaction mixture.The invention also relates to salts of bis(perfluoroalkyl)phosphinicacids and to uses thereof.

Bis(perfluoroalkyl)phosphinic acids have been known for some time andare suitable for the preparation of various chemicals, such as, forexample, corresponding methyl esters, which are strong methylatingreagents (N. V. Pavienko et al., Zh. Obshch. Khim., 59, No. 3 (1989),pages 534-537). Bis(perfluoroalkyl)phosphinic acids and theircorresponding salts are furthermore used on the basis of theirsurface-active action (DE-A 22 33 941; N. N. Kalibabchuk et al., Teor.Eksp. Khim., 11, No. 6 (1975), pages 838-841; N. N. Kalibabchuk et al.,Ukr. Khim. Zh., 44, No. 1 (1978), pages 67-70) and in fuel cells (T.Mahmood, Inorganic Chemistry, 25 (1986), pages 3128-3131).

The lithium salt of bis(pentafluoroethyl)phosphinic acid is a highlypromising candidate for use as conductive salt in lithium batteries (F.Kita et al., Proc. Electrochem. Soc., 99-25, (2000), pages 480-484; F.Kita et al., J. Power Sources, 90, No. 1 (2000), pages 27-32).

Bis(trifluoromethyl)phosphinic acid is prepared by hydrolysis ofbis(trifluoromethyl)phosphorus trichloride, which is accessible withdifficulty (H. J. Emeleus et al., J. Chem. Soc. (1955), pages 563-574).The higher homologues of bis(trifluoromethyl)phosphinic acid have beenobtained from the corresponding difluorotris(perfluoroalkyl)phosphoranes(V. Ya. Semenii et al., U.S.S.R. Patent 498,311).

The literature discloses essentially two different processes for thepreparation of bis(perfluoroalkyl)phosphinic acids.

In the first process, a difluorotris(perfluoroalkyl)phosphorane is, in afirst step, reacted with hexamethyldisiloxane to give the correspondingphosphine oxide. This is then followed in a second step by hydrolysis tothe corresponding bis(perfluoroalkyl)phosphinic acid. This process hasthe disadvantage that the temperature during the hydrolysis must becontrolled and regulated very precisely and only extremely small amountsof the desired bis(perfluoroalkyl)phosphinic acid are usually obtained(T. Mahmood, Inorganic Chemistry, 25 (1986), pages 3128-3131; U.S.S.R.Patent, 498,311; pages 57-61; T. Mahmood et al., Inorganic Chemistry, 27(1988), pages 2913-2916).

A further known process is the direct hydrolysis ofdifluorotris(perfluoroalkyl)phosphoranes tobis(perfluoroalkyl)phosphinic acids (T. Mahmood et al, InorganicChemistry, 27 (1988), pages 2913-2916). It is disadvantageous in thisprocess that, owing to the very poor miscibility of the phosphoraneswith water, in particular of the phosphoranes with long alkyl chains,the hydrolysis proceeds only very slowly and usually results in verycomplex product mixtures.

The object of the present invention was therefore to provide a processwhich enables the simple and inexpensive preparation ofbis(perfluoroalkyl)phosphinic acids in good yields. Thebis(perfluoroalkyl)phosphinic acids should preferably be obtained inhigh purity. A further object was to provide salts ofbis(perfluoroalkyl)phosphinic acids.

This object has been achieved by the process according to the inventionfor the preparation of bis(perfluoroalkyl)phosphinic acids whichcomprises at least the following process steps:

-   -   a) reaction of at least one        difluorotris(perfluoroalkyl)phosphorane or at least one        trifluorobis(perfluoroalkyl)phosphorane with hydrogen fluoride        in a suitable reaction medium, and    -   b) heating of the reaction mixture obtained in a).

Difluorotris(perfluoroalkyl)phosphoranes andtrifluorobis(perfluoroalkyl)phosphoranes can be prepared by conventionalmethods known to the person skilled in the art.

These compounds are preferably prepared by electrochemical fluorinationof suitable starting compounds, as described in V. Ya. Semenii et al.,Zh. Obshch. Khim., 55, No. 12 (1985), pages 2716-2720; N. lgnatiev, J.of Fluorine Chem., 103 (2000), pages 57-61 and WO 00/21969. Thecorresponding descriptions are hereby incorporated by way of referenceand are regarded as part of the disclosure.

It is also possible to employ mixtures of two or moredifluorotris(perfluoroalkyl)phosphoranes and/or two or moretrifluorobis(perfluoroalkyl)phosphoranes in the process according to theinvention. Preferably, in each case only onedifluorotris(perfluoroalkyl)phosphorane ortrifluorobis(perfluoroalkyl)phosphorane is employed in the processaccording to the invention.

In a preferred embodiment. of the process according to the invention,use is made of at least one difluorotris(perfluoroalkyl)phosphorane orat least one trifluorobis(perfluoroalkyl)phosphorane of the generalformula I(C_(n)F_(2n+1))_(m)PF_(5-m)where 1≦n≦8, preferably 1≦n≦4, and m in each case=2 or 3.

Particularly preferred difluorotris(perfluoroalkyl)phosphorane compoundscan be selected from the group consisting ofdifluorotris(pentafluoroethyl)phosphorane,difluorotris(n-nonafluorobutyl)phosphorane anddifluorotris(n-heptafluoropropyl)phosphorane.

A particularly preferred trifluorobis(perfluoroalkyl)phosphoranecompound which can be employed in the process according to the inventionis trifluorobis(n-nonafluorobutyl)phosphorane.

The reaction of at least one difluorotris(perfluoroalkyl)phosphorane orat least one trifluorobis(perfluoroalkyl)phosphorane with hydrogenfluoride in a suitable reaction medium is preferably carried out in aprocess as described in DE 101 30 940.6. The corresponding descriptionis hereby incorporated by way of reference and is regarded as part ofthe disclosure.

The temperature for the heating of the reaction mixture obtained inprocess step a) in process step b) is preferably from room temperatureto 150° C., particularly preferably from 100° C. to 145° C. and veryparticularly preferably from 135 to 140° C.

The reaction mixture obtained in process step a) is preferably heated inprocess step b) for from 1 to 150 hours, particularly preferably forfrom 10 to 25 hours and very particularly preferably for from 18 to 22hours.

If desired, it may be advantageous again to add some of the same oranother reaction medium to the reaction mixture during the heating inprocess step b).

In order to accelerate the hydrolysis, the reaction mixture obtained inprocess step a) can preferably also be heated in a closed,pressure-tight apparatus, such as, for example, an autoclave, atelevated temperature, preferably of from 140° C. to 200° C.

Besides the desired bis(perfluoroalkyl)phosphinic acids, the reaction inaccordance with the process according to the invention gives hydrogenfluoride and in each case the corresponding monohydroperfluoroalkane asfurther reaction products.

These reaction products can, if desired, be separated off, if desiredcollected and if desired isolated by conventional methods which arefamiliar to the person skilled in the art, for example by condensationin suitable cold traps.

Hydrogen fluoride and monohydroperfluoroalkanes are themselves valuablechemical raw materials which can be utilised usefully. Thus, it ispossible, inter alia, to collect and recycle the hydrogen fluoride sothat it is available for the reaction in process step a).

If necessary, the preparation of bis(perfluoroalkyl)phosphinic acids bythe process according to the invention can be followed by purificationand, if desired, isolation of these compounds by conventional methodswhich are familiar to the person skilled in the art.

The purification is preferably carried out by distillation, preferablyunder reduced pressure at elevated temperatures.

The respective salts of bis(perfluoroalkyl)phosphinic acid canpreferably be isolated by neutralisation ofbis(perfluoroalkyl)phosphinic acids.

The salts are prepared from the respective bis(perfluoroalkyl)phosphinicacid by reaction with at least one conventional base which is known tothe person skilled in the art, preferably in solution.

In order to prepare the salts, bis(perfluoroalkyl)phosphinic acids areneutralised using bases, preferably selected from the group consistingof the hydroxides, oxides, hydrides, amides, carbonates, phosphines andamines.

After the neutralisation, the salt formed is worked up in a manner knownto the person skilled in the art. The salt can be washed andsubsequently dried.

The application also relates to salts of bis(perfluoroalkyl)phosphinicacids selected from the group consisting of partially alkylated andperalkylated ammonium, phosphonium, sulfonium, pyridinium, pyridazinium,pyrimidinium, pyrazinium, imidazolium, pyrazolium, thiazolium, oxazoliumand triazolium salts salts. Preference is given to the preparation ofsalts of bis(perfluoroalkyl)phosphinic acids having a cation selectedfrom the group consisting of

where R¹ to R⁵ are identical or different, are optionally bondeddirectly to one another by a single or double bond and are each,individually or together, defined as follows:

-   -   H,    -   halogen, where the halogens are not bonded directly to N,    -   an alkyl radical (C₁ to C₈), which may be partially or        completely substituted by further groups, preferably F, Cl,        N(C_(n)F_((2n+1-x))H_(x))₂, O(C_(n)F_((2n+1-x))H_(x)),        SO₂(C_(n)F_((2n+1-x))H_(x)), C_(n)F_((2n+1-x))H_(x), where 1<n<6        and 0<x≦2n+1.

Surprisingly, it has been found that these salts can be used as ionicliquids, phase-transfer catalysts or surfactants.

The process according to the invention for the preparation ofbis(perfluoroalkyl)phosphinic acids enables the simple, inexpensive andreliable preparation of these compounds in very good yields.Bis(perfluoroalkyl)phosphinic acids are usually obtained in high puritywithout further complex purification steps. Through the reaction withbases, salts can be obtained which were hitherto not available

It is furthermore advantageous that the by-products obtained in theprocess according to the invention, namely hydrogen fluoride andmonohydroperfluoroalkanes, are themselves valuable raw materials whichcan be utilised usefully. This enables the environmental impact in thereaction in accordance with the process according to the invention to bekept low and the costs for the process according to the invention to bereduced.

The invention is explained below with reference to examples. Theseexamples serve merely to explain the invention and do not restrict thegeneral inventive idea.

EXAMPLES

The NMR spectra were recorded using a Bruker Avance 300 NMR spectrometerat the following frequencies:

-   -   300.1 MHz ¹H    -   282.4 MHz for ¹⁹F and    -   121.5 MHz for ³¹P.

Example 1 Synthesis of bis(pentafluoroethyl)phosphinic acid(C₂F₅)₂P(O)OH

a)

3.53 g of water (corresponding to a total amount of water in the mixtureof 294 mmol) were added to 2.93 g of 40% by weight hydrofluoric acid(corresponding to 58.6 mmol of HF) in an FEP (fluoroethylene polymer)flask. The resultant mixture was then cooled using an ice bath. 25.03 g(58.7 mmol) of difluorotris(pentafluoroethyl)phosphorane, (C₂F₅)₃PF₂,were subsequently added over the course of 3 minutes with stirring usinga magnetic stirrer. The difluorotris(pentafluoroethyl)phosphoranedissolved completely within a further three minutes, and a colourless,clear solution of H⁺[(C₂F₅)₃PF₃]⁻ in water was obtained.

The resultant solution was stirred at room temperature for a further 15minutes and subsequently refluxed at an oil-bath temperature of from 135to 140° C. for 14 hours. A further 4.83 g of water were subsequentlyadded to the solution, and the mixture was refluxed at the sametemperature for a further 6 hours. After cooling to room temperature,24.81 g of a clear solution were obtained.

3.95 g of a two-phase liquid were collected in an intermediate trapcooled with dry ice. This liquid comprised 2.11 g of C₂F₅H, 1.5 g of HFand 0.34 g of the starting compounddifluorotris(pentafluoroethyl)phosphorane.

In order to isolate bis(pentafluoroethyl)phosphinic acid, aqueous.hydrogen fluoride solution was distilled off from the reaction mixture,giving 15.13 g of virtually pure bis(pentafluoroethyl)phosphinic acid.The yield was 86.5%, based on thedifluorotris(pentafluoroethyl)phosphorane employed.

For further purification, the bis(pentafluoroethyl)phosphinic acid wasdistilled under reduced pressure at 125.Pa. The boiling point was 63-64°C.

The resultant bis(pentafluoroethyl)phosphinic acid was characterised bymeans of ¹⁹F—, ³¹P— and ¹H-NMR spectroscopy and by elemental analysis:

¹⁹F-NMR spectrum; δ, ppm:

(solvent acetone-D₆, reference CCl₃F)

−80.55 s (CF₃); −125.37 d (CF₂); J² _(P,F)=78.2 Hz

¹H-NMR spectrum; δ, ppm:

(solvent acetone-D₆, reference TMS)

12.71 br. s (OH)

³¹P-NMR spectrum; δ, ppm:

(solvent acetone-D₆, reference 85% by weight H₃PO₄)

−0.03 quin; J² _(P,F)=78.3 Hz

The values of the chemical shifts found correspond to the valuesdisclosed in the publication by T. Mahmood, Inorganic Chemistry, 25(1986), pages 3128-3131.

Elemental analysis: Found: C, 15.76%; H, 0.40%. Calculated for((C₂F₅)₂P(O)OH): C, 15.91%; H, 0.33%.

b)

2.50 g of water (corresponding to a total amount of water in the mixtureof 166.5 mmol) were added to 0.834 g of a 40% by weight aqueoushydroflouric acid (corresponding to 16.7 mmol of HF) in an FEP flask.The resultant mixture was then cooled using an ice bath. 7.11 g (16.7mmol) of difluorotris(pentafluoroethyl)phosphorane, (C₂F₅)₃PF₂, werefinally added over the course of three minutes with stirring using amagnetic stirrer. The difluorotris(pentafluoroethyl)phosphoranedissolved completely within a further three minutes, and a colourless,clear solution of H⁺[(C₂F₅)₃PF₃]⁻ in water was obtained. The reactionmixture was refluxed at an oil-bath temperature of 115° C.-120° C. for108 hours. In order to isolate the bis(pentafluoroethyl)phosphinic acid,water/HF solution were distilled off from the reaction mixture, giving3.97 g of virtually pure bis(pentafluoroethyl)phosphinic acid,(C₂F₅)₂P(O)OH. The yield was 78.8%, based on thedifluorotris(pentafluoroethyl)phosphorane employed. The resultantproduct was characterised by means of ¹⁹F-NMR spectroscopy. Thecorresponding signals corresponded to the signals mentioned underExample 1a.

c)

2.59 g (56.2 mmol) of ethanol were cooled in an FEP vessel using an icebath. Firstly 0.49 g (24.5 mmol) of hydrogen fluoride (HF) was slowlyadded to the ethanol with stirring using a magnetic stirrer, and 9.59 g(22.5 mmol) of difluorotris(pentafluoroethyl)phosphorane, (C₂F₅)₃PF₂,were added to the reaction mixture over the course of a further threeminutes. After the phosphorane had dissolved, 2.21 g (122.6 mmol) ofwater were added to the solution, and the reaction mixture were refluxedat an oil-bath temperature of 120° C. for 144 hours (2.1 g of water wereadded to the reaction mixture after. 44 hours and a further 2.0 g ofwater were added after 94 hours).

In order to isolate the bis(pentafluoroethyl)phosphinic acid,ethanol/water/HF solution were distilled off from the reaction mixture,giving 5.21 g of virtually pure bis(pentafluoroethyl)phosphinic acid,(C₂F₅)₂P(O)OH. The yield was 76.6%, based on thedifluorotris(pentafluoroethyl)phosphorane employed. The resultantproduct was characterised by means of ¹⁹F-NMR spectroscopy. Thecorresponding signals corresponded to the signals indicated underExample 1a.

Example 2 Synthesis of bis(n-nonafluorobutyl)phosphinic acid(n-C₄F₉)₂P(O)OH

a)

4.25 g of water (corresponding to a total amount of water in the mixtureof 371 mmol) were added to 4.07 g of a 40% by weight hydrofluoric acid(corresponding to 81.4 mmol of HF) in an FEP (fluoroethylene polymer)flask. The resultant mixture was then cooled using an ice bath. 51.42 g(70.8 mmol) of difluorotris(n-nonafluorobutyl)phosphorane, (n-C₄F₉)₃PF₂,were subsequently added over the course of 10 minutes with stirringusing a magnetic stirrer.

The resultant solution was stirred at room temperature for a further 20minutes and subsequently refluxed at an oil-bath temperature of from 135to 140° C. for 11.5 hours. A further 5.00 g of water were subsequentlyadded to the solution, and the mixture was refluxed at the sametemperature for a further 8.5 hours. After cooling to room temperature,46.47 g of a clear solution were obtained. 15.03 g of a two-phase liquidwere collected in an intermediate trap cooled with dry ice. This liquidcomprised 13.06 g of n-C₄F₉H and 1.97 g of HF (upper phase).

In order to isolate the bis(n-nonafluorobutyl)phosphinic acid, aqueoushydrogen fluoride solution was distilled off from the reaction mixtureat an oil-bath temperature of 145° C., giving 34.62 g of virtually purebis(n-nonafluorobutyl)phosphinic acid as a solid. The yield was 97.4%,based on the difluorotris(n-nonafluorobutyl)phosphorane employed.

For further purification, the bis(n-nonafluorobutyl)phosphinic acid wasdistilled under reduced pressure at 125 Pa. The boiling point was 124°C. During cooling, the resultant bis(n-nonafluorobutyl)phosphinic acidsolidifies to give a solid having a melting point of 103-104° C.

In the literature publication by T. Mahmood, Inorganic Chemistry, 25(1986), pages 3128-3131, bis(n-nonafluorobutyl)phosphinic acid isdescribed as a non-volatile liquid, which is probably a hydrated form ofthis compound.

Bis(n-nonafluorobutyl)phosphinic acid was characterised by means of¹⁹F—, ³¹P— and ¹H-NMR spectroscopy and by elemental analysis:

¹⁹F-NMR spectrum; δ, ppm:

(solvent acetone-D₆, reference CCl₃F)

−80.90 t (CF₃); −120.50 br. s (CF₂); −121.38 d (CF₂); −125.58 m (CF₂);J² _(P,F)=79.5 Hz, J⁴ _(F,F)=9.9 Hz

¹H-NMR spectrum; δ, ppm:

(solvent acetone-D₆, reference TMS)

9.25 br. s (OH)

³¹P-NMR spectrum; δ, ppm:

(solvent acetone-D₆, reference 85% by weight H₃PO₄)

1.74 quin; J² _(P,F)=79.0 Hz

The values of the chemical shifts found correspond to the valuesdisclosed in the publication by T. Mahmood, Inorganic Chemistry, 25(1986), pages 3128-3131.

Elemental analysis: Found: C, 19.05%; H, 0.20%. Calculated for((n-C₄F₉)₂P(O)OH): C, 19.14%; H, 0.20%.

b)

1.45 g of water (corresponding to a total amount of water in the mixtureof 116.1 mmol) were added to 1.08 g of a 40% by weight aqueoushydroflouric acid (corresponding to 21.6 mmol of HF) in an FEP flask.The resultant mixture was then cooled using an ice bath. 7.98 g (15.2mmol) of trifluorobis(n-nonafluorobutyl)phosphorane, (C₄F₉)₂PF₃, werefinally added over the course of 10 minutes with stirring using amagnetic stirrer. The reaction mixture was stirred at room temperaturefor 15 hours and subsequently refluxed at an oil-bath temperature of110° C. for 35 hours (a further 0.6 g of water was added to the reactionmixture after 17 hours and a further 1.2 g of water were added after 25hours). In order to isolate the bis(n-nonafluorobutyl)phosphinic acid,water/HF solution were distilled off from the reaction mixture, giving6.34 g of virtually pure bis(n-nonafluorobutyl)phosphinic acid. Theyield was 83.2%, based on the trifluorobis(n-nonafluorobutyl)phosphoraneemployed. The resultant product was characterised by means of ¹⁹F-NMRspectroscopy. The corresponding signals corresponded to the signalsmentioned under Example 2a.

Example 3

3.07 g of the bis(pentafluoroethyl)phosphinic acid prepared as describedin Example 1 were neutralised in 50 cm³ of water using 7.48 g of a 20%by weight aqueous solution of tetraethylammonium hydroxide. The waterwas subsequently evaporated off, and the resultant residue was driedunder reduced pressure of 120 Pa at 70° C. (bath temperature).

4.38 g of white solid of tetraethylammoniumbis(pentafluoroethyl)phosphinate having a melting point of 100-102° C.were obtained. The yield is virtually quantitative, based on thebis(pentafluoroethyl)phosphinic acid employed.

The tetraethylammonium bis(pentafluoroethyl)phosphinate wascharacterised by means of ¹⁹F—, ³¹P— and ¹H-NMR spectroscopy and byelemental analysis:

¹⁹F-NMR spectrum; δ ppm:

(solvent acetone-D₆, reference CCl₃F)

−80.23 s (CF₃); −124.90 d (CF₂); J² _(P,F)=64.8 Hz

¹H-NMR spectrum; δ, ppm:

(solvent acetone-D₆, reference TMS)

1.36 tm (CH₃); 3.48 q (CH₂); J³ _(H,H)=7.3 Hz

³¹P-NMR spectrum; δ, ppm:

(solvent acetone-D₆, reference 85% by weight H₃PO₄)

0.28 quin, J² _(P,F)=64.5 Hz

Elemental analysis: Found: C, 33.36%; H, 4.60%; N, 3.22%. Calculated for(C₂F₅)₂P(O)ON(C₂H₅)₄: C, 33.42%; H, 4.67%; N, 3.25%.

Example 4

2.52 g of bis(pentafluoroethyl)phosphinic acid prepared as described inExample 1 were neutralised in 20 cm³ of water using 0.577 g of potassiumcarbonate. The water was subsequently evaporated, and the resultantresidue was dried under reduced pressure at 120 Pa and a bathtemperature of 100° C. 2.83 g of white solid of potassiumbis(pentafluoroethyl)phosphinate were obtained. The yield is virtuallyquantitative, based on the bis(pentafluoroethyl)phosphinic acidemployed. The salt decomposed at a temperature of 203-205° C.

The potassium bis(pentafluoroethyl)phosphinate was characterised bymeans of ¹⁹F— and ³¹P-NMR spectroscopy and by elemental analysis:

¹⁹F-NMR spectrum; δ, ppm:

(solvent acetone-D₆, reference CCl₃F)

−80.40 m (CF₃); −125.11 d (CF₂); J² _(P,F)=67.4 Hz

³¹P-NMR spectrum; δ, ppm:

(solvent acetone-D₆, reference 85% by weight H₃PO₄)

0.73 quin; J² _(P,F)=67.2 Hz

Elemental analysis: Found: C, 14.6%. Calculated for (C₂F₅)₂P(O)OK: C,14.13%.

Example 5

4.00 g of bis(n-nonafluorobutyl)phosphinic acid prepared as described inExample 2 were neutralised in 50 cm³ of water using 5.86 g of a 20% byweight aqueous solution of tetraethylammonium hydroxide. In the process,a white precipitate formed, which was filtered off and dried underreduced pressure of 120 Pa and at a bath temperature of 70° C. 4.93 g ofwhite solid of tetraethylammonium bis(n-nonafluorobutyl)phosphinatehaving a melting point of 99-100° C. were obtained. The yield was 98%,based on the bis(n-nonafluoroethyl)phosphinic acid employed.

The tetraethylammonium bis(n-nonafluorobutyl)phosphinate wascharacterised by means of ¹⁹F—, ³¹P— and ¹H-NMR spectroscopy and byelemental analysis:

¹⁹F-NMR spectrum; δ, ppm:

(solvent acetone-D₆, reference CCl₃F)

−80.75 tt (CF₃); −120.35 m (CF₂); −121.17 dm (CF₂); −125.30 m (CF₂); J²_(P,F)=65.0 Hz; J⁴ _(F,F)=9.9 Hz, J_(F,F)=3.1 Hz

¹H-NMR spectrum; δ, ppm:

(solvent acetone-D₆, reference TMS)

1.37 tm (CH₃); 3.48 q (CH₂); J³ _(H,H)=7.3 Hz

³¹P-NMR spectrum; δ, ppm:

(solvent acetone-D₆, reference 85% by weight H₃PO₄)

1.70 quin; J² _(P,F)=64.9 Hz

Elemental analysis: Found: C, 30.32%; H, 3.05%, N, 2.10. Calculated for(n-C₄F₉)₂P(O)ON(C₂H₅)₄: C, 30.44%; H, 3.19%; N, 2.22.

Example 6

1.93 g (6.39 mmol) of bis(pentafluoroethyl)phosphinic acid prepared asdescribed in Example 1 were neutralised in 50 cm³ of water using asolution of 0.371 g (3.19 mmol) of 1,6-diaminohexane in 15 cm³ of water.The water was evaporated off, and the resultant residue was dried underreduced pressure at 120 Pa and a bath temperature of 100° C. 2.21 g ofwhite solid of hexamethylene-1,6-diammoniumbis(pentafluoroethyl)phosphinate having a melting point of 208-210° C.were obtained. The yield was 96.1%, based on thebis(pentafluoroethyl)phosphinic acid employed.

The hexamethylene-1,6-diammonium bis(pentafluoroethyl)phosphinate wascharacterised by means of ¹⁹F—, ³¹P— and ¹H-NMR spectroscopy and byelemental analysis:

¹⁹F-NMR spectrum; δ, ppm:

(solvent DMSO-D₆, reference CCl₃F)

−79.59 m (CF₃); −124.66 ppm d (CF₂); J² _(P,F)=65.6 Hz

¹H-NMR spectrum; δ ppm:

(solvent DMSO-D₆, reference TMS)

1.30 m (2CH₂); 1.51 m (2CH₂); 2.76 m (2CH₂), 7.53 br. s (2NH₃ ⁺)

³¹P-NMR spectrum; δ, ppm:

(solvent DMSO-D₆, reference substance 85% by weight H₃PO₄)

−2.15 quin; J² _(P,F)=65.5 Hz

Elemental analysis: Found: C, 23.61%; H, 2.49%; N, 4.07%. Calculated for[(C₂F₅)₂P(O)O]₂ ²⁻[H₃N(CH₂)₆NH₃]²⁺ C, 23.35%; H, 2.52%; N, 3.89%.

Example 7

2.80 g (5.58 mmol) of bis(n-nonafluorobutyl)phosphinic acid prepared asdescribed in Example 2 were neutralised in 50 cm³ of water using asolution of 0.324 g (2.79 mmol) of 1,6-diaminohexane in 15 cm³ of water.In the process, a white precipitate formed, which was filtered off anddried under reduced pressure at 120 Pa and a bath temperature of 100° C.2.87 g of white solid of hexamethylene-1,6-diammoniumbis(n-nonafluorobutyl)phosphinate having a melting point of >250° C.were obtained. The yield was 92%, based on thebis(n-nonafluorobutyl)phosphinic acid employed.

The hexamethylene-1,6-diammonium bis(n-nonafluorobutyl)phosphinate wascharacterised by means of ¹⁹F—, ³¹P— and ¹H-NMR spectroscopy and byelemental analysis:

¹⁹F-NMR spectrum; δ, ppm:

(solvent DMSO-D₆, reference CCl₃F)

−80.03 t (CF₃); −120.46 m (CF₂); −121.28 dm (CF₂), −125.11 m (CF₂), J²_(P,F)=65.6 Hz, J⁴ _(F,F)=9.5 Hz

¹H-NMR spectrum; δ, ppm:

(solvent DMSO-D₆, reference TMS)

1.29 m (2CH₂); 1.51 m (2CH₂); 2.76 m (2CH₂), 7.61 br. s (2NH₃ ⁺)

³¹P-NMR spectrum; δ, ppm:

(solvent DMSO-D₆, reference 85% by weight H₃PO₄)

−0.76 quin; J² _(P,F)=65.5 Hz

Elemental analysis: Found: C, 23.76%; H, 1.58%; N, 2.48%. Calculatedfor: [(C₄F₉)₂P(O)O]₂ ²⁻[H₃N(CH₂)₆NH₃]²⁺ C, 25.59; H, 1.62%; N, 2.50%.

Example 8

2.23 g (4.44 mmol) of bis(n-nonafluorobutyl)phosphinic acid prepared asdescribed in Example 2 were neutralised in 50 cm³ of water using asolution of 1.20 g (4.45 mmol) of tri-n-hexylamine in 20 cm³ of a 1:1(vol/vol) water/ethanol mixture. 15 cm³ of ethanol were subsequentlyadded, and the mixture was refluxed for 5 minutes.

After cooling to room temperature, a white precipitate formed, which wasfiltered off and dried under reduced pressure at 120 Pa and a bathtemperature of 60° C. 3.22 g of white solid of tri-n-hexylammoniumbis(n-nonafluorobutyl)phosphinate having a melting point of 74-75° C.were obtained. The yield was 93.9%, based on thebis(n-nonafluorobutyl)phosphinic acid employed.

The tri-n-hexylammonium bis(n-nonafluorobutyl)phosphinate wascharacterised by means of ¹⁹F—, ³¹P— and ¹H-NMR spectroscopy and byelemental analysis:

¹⁹F-NMR spectrum; δ, ppm:

(solvent acetone-D₆, reference CCl₃F)

−80.82 tt (CF₃); −120.36 m (CF₂); −121.32 dm (CF₂), −125.53 m (CF₂); J²_(P,F)=70.1 Hz; J⁴ _(F,F)=9.9 Hz, J_(F,F)=3.0 Hz

¹H-NMR spectrum; δ, ppm:

(solvent acetone-D₆, reference TMS)

0.89 m (3CH₂); 1.35 m (9CH₂); 1.82 m (3CH₂); 3.21 m (2CH₂); 9.62 br. s(NH⁺)

³¹P-NMR spectrum; δ, ppm:

(solvent acetone-D₆, reference 85% by weight H₃PO₄)

1.76 quin; J² _(P,F)=70.1 Hz

Elemental analysis: Found: C, 40.51%; H, 5.20%; N, 1.80%. Calculated for(C₄F₉)P(O)O⁻ ⁺HN(C₆H₁₃)₃: C, 40.45%; H, 5.22%; N, 1.82%.

Example 9

1.55 g (3.09 mmol) of bis(n-nonafluorobutyl)phosphinic acid prepared asdescribed in Example 2 in 15 cm³ of water are mixed with a solution of1.20 g (3.09 mmol) of triphenylbenzylphosphonium chloride in 30 cm³ ofwater, and the mixture is stirred at room temperature for 5 minutes. Inthe process, a white precipitate formed, which is filtered off and driedunder reduced pressure at 120 Pa and a bath temperature of 60° C. 2.50 gof white solid of triphenylbenzylphosphoniumbis(n-nonafluorobutyl)phosphinate having a melting point of 138-139° C.are obtained. The yield is 95.1% on the bis(n-nonafluorobutyl)phosphinicacid employed.

Triphenylbenzylphosphonium bis(n-nonafluorobutyl)phosphinate ischaracterised by means of ¹⁹F—, ³¹P— and ¹H-NMR spectroscopy and byelemental analysis:

¹⁹F NMR spectrum, δ, ppm:

(solvent: acetone-D6 ; reference: CCl₃F):

−80.76 t (CF₃); −120.36 m (CF₂); −121.21 dm (CF₂); −125.38 m (CF₂); J²_(P,F)=65.9 Hz, J⁴ _(F,F)=9.9 Hz.

¹H NMR spectrum, 67 , ppm:

(solvent: acetone-D6 ; reference: TMS):

5.22 d (CH₂, PhCH₂); 7.11-7.17 m (2H, PhCH₂); 7.19-7.27 m (2H, PhCH₂)

7.30-7.37 m (iH, PhCH₂); 7.72-7.87 m (12H, 3Ph); 7.91-7.99 m (3H, 3Ph)J² _(P,H)=15.1 Hz.

³¹P NMR spectrum, δ, ppm:

(solvent: acetone-D6; reference: 85% by weight H₃P0₄):

1.78 quin; 25.68 br.s; J² _(P,F)=65.8Hz.

Elemental analysis: Found: C, 46.10%; H, 2.48%. Calculated for[(C₄F₉)₂P(O)O]⁻[(C₆H₅)₃C₆H₅CH₂P]⁺: C, 46.39%; H, 2.60%.

Example 10

A solution of 2.08 g (11.9 mmol) of 1-butyl-3-methylimidazoliumchlorides in 3 cm³ of water is added at room temperature to 4.05 g (11.9mrnol) of the potassium bis(pentafluoroethyl)phosphinate prepared asdescribed in Example 4 in 15 cm³ of water with constant stirring. In theprocess, an oily precipitate formed. The water is evaporated off underreduced pressure, and the resultant residue is dried under reducedpressure of 120 Pa and a bath temperature of 60° C. for 1 hour. 10 cm³of isopropyl alcohol are subsequently added to the residue, and a whiteprecipitate is filtered off and washed twice with 5 cm³ of isopropylalcohol. The isopropyl alcohol is evaporated off under reduced pressure,and the resultant residue is dried under reduced pressure of 120 Pa anda bath temperature of 80° C. for 2 hours.

4.99 g of an oily liquid of 1-butyl-3-methylimidazoliumbis(pentafluoroethyl)phosphinate are obtained. The yield is 95.4%, basedon the potassium bis(pentafluoroethyl)phosphinate employed.

1 -Butyl-3-methylimidazolium bis(pentafluoroethyl)phosphinate wascharacterised by means of ¹⁹F, ³¹P and ¹H-NMR spectroscopy:

¹⁹F NMR spectrum, ppm:

(solvent: acetonitrile-D₃; reference: CCl₃F):

−80.19 m (CF₃); −124.93 d (CF₂); J² _(P,F)=66.9 Hz.

¹H NMR spectrum, ppm:

(solvent: acetonitrile-D₃; reference: TMS):

0.93 t (3H, CH₃); 1.33 tq (2H, CH₂); 1.83 tt (2H, CH₂); 3.87 s (3H,CH₃);

4.17 t (2H, CH₂); 7.48 dd (1H) 7.54 dd (1H); 8.99 s (1H); J³ _(H,H)=1.6Hz; J³ _(H,H)=7.3 Hz; J³ _(H,H)=7.6 Hz.

³¹P NMR spectrum, ppm:

(solvent: acetonitrile-D₃; reference: 85% H₃PO₄):

−1.86 quin; J² _(P,F)=66.8 Hz.

1. Process for the preparation of bis(perfluoroalkyl)phosphinic acids orsalts thereof comprising at least the following process steps: a)reaction of at least one difluorotris(perfluoroalkyl)phosphorane or atleast one trifluorobis(perfluoroalkyl)phosphorane with hydrogen fluoridein a suitable reaction medium, and b) heating of the reaction mixtureobtained in a).
 2. Process for the preparation ofbis(perfluoroalkyl)phosphinic acids or salts thereof according to claim1, characterised in that the salts are prepared by subsequentneutralisation.
 3. Process according to claim 1, characterised in thatthe difluorotris(perfluoroalkyl)phosphorane ortrifluorobis(perfluoroalkyl)phosphorane employed is a compound of thegeneral formula I(C_(n)F_(2n+1))_(m)PF_(5-m) in which 1≦n≦8, preferably 1≦n≦4, and m ineach case=2 or
 3. 4. Process according to claim 1, characterised in thatthe difluorotris(perfluoroalkyl)phosphorane employed is a compoundselected from the group consisting ofdifluorotris(pentafluoroethyl)phosphorane,difluorotris(n-nonafluorobutyl)phosphorane anddifluorotris(n-heptafluoropropyl)phosphorane.
 5. Process according toclaim 1, characterised in that thetrifluorobis(perfluoroalkyl)phosphorane compound employed istrifluorobis(n-nonafluorobutyl)phosphorane. nonafluorobutyl)phosphorane.6. Process according to claim 1, characterised in that the temperatureduring the heating in process step b) is from room temperature to 150°C., preferably from 100° C. to 145° C., particularly preferably from 135to 140° C.
 7. Process according to claim 1, characterised in that theduration of the heating in process step b) is from 1 to 150 hours,preferably from 10 to 25 hours, particularly preferably from 18 to 22hours.
 8. Process according to claim 1, characterised in that thereaction medium is water or a water-based mixture.
 9. Process accordingto claim 2, characterised in that bases, preferably hydroxides, oxides,hydrides, amides, carbonates, phosphines or amines, are used to preparethe salts.
 10. Salts of bis(perfluoroalkyl)phosphinic acids selectedfrom the group consisting of partially alkylated and peralkylatedammonium, phosphonium, sulfonium, pyridinium, pyridazinium,pyrimidinium, pyrazinium, imidazolium, pyrazolium, thiazolium, oxazoliumand triazolium salts salts.
 11. Salts of bis(perfluoroalkyl)phosphinicacids according to claim 10, having a cation selected from the groupconsisting of

where R¹ to R⁵ are identical or different, are optionally bondeddirectly to one another by a single or double bond and are each,individually or together, defined as follows: H, halogen, where thehalogens are not bonded directly to N, an alkyl radical (C₁ to C₈),which may be partially or completely substituted by further groups,preferably F, Cl, N(C_(n)F_((2n+1-x))H_(x))₂, O(C_(n)F_((2n+1-x))H_(x)),SO₂(C_(n)F_((2n+1-x))H_(x)), C_(n)F_((2n+1-x))H_(x), where 1<n<6 and0<x≦2n+1.
 12. Use of the salts of bis(perfluoroalkyl)phosphinic acidsaccording to claim 10 as ionic liquids.
 13. Use of the salts ofbis(perfluoroalkyl)phosphinic acids according to claim 10 asphase-transfer catalyst or surfactants.